The present invention is directed to liquid developer compositions. More specifically, the present invention is directed to liquid developers comprising a liquid medium, a charge control agent, a polymeric surfactant and a colored core polymer. The colored core polymer of the present invention is of the formula ##STR3## wherein A is selected from the group consisting of alkylene and arylene, B is selected from the group consisting of ##STR4## wherein R is an alkylene group, an arylene group, or a polyether segment, D is selected from the group consisting of dioxyalkane and dioxyarene, x is a fraction number of from about 0.01 to 1.0, and y is a fraction number of from 0 to about 0.99, with x+y being equal to 1, and n representing the number of the monomer units.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basis electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Development of electrostatic latent images with liquid developer compositions is also known. Liquid electrophotographic developers generally comprise a liquid vehicle in which is dispersed charged colored toner particles. In liquid development processes, the photoreceptor bearing the electrostatic latent image is contacted with the liquid developer. Contact with the charged areas of the photoreceptor causes the charged toner particles present in the liquid vehicle to migrate through the liquid to the charged areas of the photoreceptor to develop the latent image. Thereafter, the photoreceptor is withdrawn from the liquid developer with the charged colored particles adhering to the electrostatic latent image in image configuration. The developed image is then typically transferred to a suitable substrate, such as paper or transparency material, and, optionally, may be fixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Colored particles in liquid electrophotographic developers frequently comprise pigmented resin particles, wherein either the pigment particles are dispersed in larger resin particles or pigment particles are coated with a resin. One difficulty that can arise with developers containing pigmented resin particles is inhomogeneous distribution and dispersion of the pigment particles within the resin, which can result in poor image color fidelity. In addition, liquid developers containing pigmented resin particles can form images wherein the pigment smears, which results primarily from weak binding of the pigment to the print substrate by the polymer. Further, pigments and pigmented particles tend to exhibit poor color mixing properties, which can impair image color quality. In addition, colored particles in liquid electrophotographic developers can comprise dyed polymeric particles, wherein the dye is imbibed into the polymeric particles. One difficulty that can arise with developers containing dyed polymeric particles is diffusion of the dye from the polymeric particle into the liquid vehicle of the developer, which results in undesirable background coloration of developed images.
Liquid developers of the present invention contain colored polymers as the colorant and the binding vehicle instead of conventional pigment/binder resin particles or dyed polymeric particles as typically employed in known liquid developers. The liquid developers of the present invention exhibit resistance to color smearing, since the colorant is also the binder material and no separation of colorant from binder polymer can occur. In addition, since the colorants of the liquid developers of the present invention are dyes covalently bound within a polymeric structure, the developers exhibit improved color mixing properties as a result of the dye-based colorant instead of a pigment-based colorant. Further, liquid developers of the present invention form images that exhibit excellent waterfastness because of the water insolubility of the colored polymeric particles of the developer. The liquid developers of the present invention also exhibit high color fidelity resulting from homogeneous dispersion of the colorant within the colored particles. In addition, the liquid developers of the present invention do not exhibit coloration of the liquid vehicle as a result of dye molecules diffusing from dyed polymeric particles, since the dye is an integral portion of the polymeric particles and is covalently bound thereto. Liquid developers of the present invention also have low toxicity compared to developers containing polymeric particles with dye molecules imbibed therein, since dye molecules, which are frequently toxic, do not diffuse from the particles into the liquid vehicle of the present invention.
Colored polymeric materials are known. For example, U.S. Pat. No. 4,375,357 (Wingard, Jr. et al.) discloses a family of water-soluble noncrystalline polymeric black colorants composed of an organic polymer backbone with a plurality of aromatic rings from which depend via azo. groups a plurality of chromophore units. The water-soluble polymeric colorants form dyes and inks that are fast to paper stock.
In addition, U.S. Pat. No. 4,645,727 (Ong et al.) the disclosure of which is totally incorporated herein by reference, discloses a dry toner comprising resin particles and covalently bonded polymeric dye chromophores of the formula ##STR5## wherein A is selected from the group consisting of alkylene and arylene, B is selected from the group consisting of ##STR6## wherein R is an alkylene group, an arylene group, or a polyether segment, D is selected from the group consisting of dioxyalkane and dioxyarene, x is a fraction number of 0.01 to 0.50, and y is a fraction number of 0.50 to 0.99, with x+y being equal to 1.
Further, U.S. Pat. No. 4,778,742 (Ong et al.), the disclosure of which is totally incorporated herein by reference, discloses a dry toner comprising resin particles and polymeric dye components of the formula ##STR7## wherein A is selected from the group consisting of alkylene and arylene, B is selected from the group consisting of ##STR8## wherein R is selected from the group consisting of an alkylene group, an arylene group, and a polyether group, and x represents a number of from 2 to about 100.
Although the known compositions are suitable for their intended purposes, a need remains for liquid developers that exhibit resistance to color smearing. In addition, there is a need for liquid developers that exhibit improved color mixing properties. Further, there is a need for liquid developers that form images which exhibit excellent waterfastness. A need also exists for liquid developers that exhibit high color fidelity. There is also a need for liquid developers containing colored particles exhibiting homogeneous dispersion of the colorant within the particles. Further, a need exists for liquid developers with improved lightfastness characteristics. In addition, there is a need for liquid developers having the advantages of a developer containing dyed particle but which does not exhibit diffusion of the dye into the liquid vehicle, thereby improving image quality and reducing background coloration of developed images. There is also a need for liquid developers having the advantages of a developer containing dyed particle but which does not exhibit diffusion of the dye into the liquid vehicle, thereby greatly improving the toxicological properties of the developer. Additionally, there is a need for developers with the above noted advantages that can be employed in liquid development processes, thereby enabling development of images of superior quality and resolution.